Skin is the soft outer covering of animals. In mammals, the skin is the largest organ of the integumentary system and is made up of multiple layers of ectodermal tissue. Because it interfaces with the environment, the skin has the important function of protecting the underlying muscles, bones, ligaments and internal organs from outside contact or injury. The skin further plays a key role in protecting the body against pathogens and excessive water loss. Among the skin's other functions are thermal insulation and regulation, gas absorption, sensation (the skin contains nerve endings that respond to heat and cold, touch, pressure, vibration, and tissue injury), and synthesis of vitamin D folates.
The skin may be affected by disorders or diseases that are diverse in terms of cause, presentation and/or treatment. Among the most common skin disorders or diseases are dermatitis/eczema, psoriasis and itching.
Dermatitis is generally caused by an allergic reaction to specific allergens. The term “dermatitis” is often used interchangeably with the term “eczema,” which is also called dermatitis eczema or eczematous dermatitis. Dermatitis comprises conditions such as: contact dermatitis (caused by an allergen or an irritating substance); atopic dermatitis; dermatitis herpetiformis (which appears as a result of celiac disease); seborrheic dermatitis; nummular dermatitis (which tends to appear more frequently in middle-aged people); stasis dermatitis (an inflammation on the lower legs which is caused by buildups of blood and fluid and more likely to occur in people with varicose); and perioral dermatitis (which is similar to rosacea and often observed in women between 20 and 60 years old).
Dermatitis symptoms range from skin rashes to bumpy rashes, including blisters. Although every type of dermatitis has different symptoms, there are presentations that are common for all of them, including redness of the skin, swelling, itching, skin lesions and sometimes oozing and scarring. Also, the area of the skin on which the symptoms appear may be different with each type of dermatitis. The symptoms of contact dermatitis usually appear at the site where the allergen got into contact with the skin. Although the symptoms of atopic dermatitis vary from person to person, the most common symptoms are dry, itchy, red skin. Typically affected skin areas include the folds of the arms, the back of the knees, wrists, face and hands. Less commonly there may be cracks behind the ears, and various other rashes on any part of the body. Itching is the primary symptoms of this condition.
Treatment of dermatitis is made accordingly with the particular cause of the disease. Application of corticosteroidal creams or wet compresses and avoidance of allergens and irritants are part of most treatment plans. For some types of dermatitis, non-steroidal medications and occasional use of over-the-counter antihistamines may help relieve signs and symptoms.
Psoriasis is a chronic immune-mediated skin disease that appears when the immune system sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is not contagious and is commonly seen as red and white hues of scaly patches (plaques) appearing on the top first layer of the epidermis. Some patients, though, have no dermatological symptoms. Plaques frequently occur on the skin of the elbows and knees, but can affect any area, including the scalp, palms of hands and soles of feet, and genitals. In contrast to eczema, psoriasis is more likely to be found on the outer side of the joint.
Psoriasis is a chronic recurring condition that varies in severity from minor localized patches to complete body coverage. Fingernails and toenails are frequently affected (psoriatic nail dystrophy) and can be seen as an isolated symptom. Psoriasis can also cause inflammation of the joints, which is known as psoriatic arthritis. Between 10% and 40% of all people with psoriasis have psoriatic arthritis.
The cause of psoriasis is not fully understood, but it is believed to have a genetic component and local psoriatic changes can be triggered by an injury to the skin. Various environmental factors have been suggested as aggravating to psoriasis, including stress and withdrawal of systemic corticosteroid. There are treatments available (such as topical agents, phototherapy, and systemic agents, such as methotrexate, cyclosporine and retinoids) but psoriasis treatment is challenging because of the chronic recurrent nature of the disease.
Itching is a sensation that causes the desire or reflex to scratch. The behavioral response patterns of pain and itching are intrinsically different: pain creates a withdrawal reflex, while itch leads to a scratch reflex. Umnyelinated nerve fibers for itch and pain both originate in the skin; however, information for them is conveyed centrally in two distinct systems that both use the same peripheral nerve bundle and spinothalamic tract. Itching may be triggered by infections and infestations, environmental and allergic triggers, dermatological disorders (such as dry skin, psoriasis, eczema, sunburn, topical fungal infections (such as but not limited to athlete's foot, ringworm, and onychomycosis), hidradenitis suppurativa, scab healing, scar growth, development or emergence of moles, pimples and ingrown hairs from below the epidermis, punctate palmoplantar keratoderma and dandruff), medical disorders (malignancy or internal cancer such as lymphoma and Hodgkin's disease), jaundice and cholestasis, polycythemia, thyroid illness, hyperparathyroidism, uraemia, diabetes mellitus, iron deficiency anemia, menopause or changes in hormonal balances associated with aging), medication (morphine and other opiates, chloroquine) and conditions related to pregnancy (intrahepatic cholestasis of pregnancy, pruritic urticarial papules and plaques of pregnancy (PUPPP) and gestational pemphigoid).
Itching is often treated with over-the-counter and prescription anti-itch drugs, such as antihistamines (such as diphenhydramine), corticosteroids (such as hydrocortisone topical cream), counterirritants (such as mint oil, menthol, or camphor), and crotamiton. Phototherapy is helpful for severe itching, especially if caused by renal failure.
Volatile anesthetics have been used safely for decades as general anesthetics. Recently, volatile anesthetics have been shown to be useful in the treatment of pain by administration routes rather than inhalation. For example, International Application Publication No. WO 2009/094460 discloses compositions and methods useful for reducing pain in a subject in need thereof by delivering a volatile anesthetic in a solution or an emulsion to the subject. Besides producing analgesia, volatile anesthetics affect other receptors and have been shown to have anti-inflammatory and muscle relaxing properties. For example, International Application Publication No. WO 2010/129686 discloses compositions and methods useful for treating inflammation or a wound in a subject in need of such wound treatment or inflammation treatment by delivering a volatile anesthetic to the wound or the inflammation site. Volatile anesthetics have been further shown to reduce cytokine production and release in both in vivo and in vitro inflammation model, and downregulate lipopolysaccharide (LPS)-induced production of pro-inflammatory cytokines. Additionally, volatile anesthetics have been shown to inhibit neutrophil function and decrease time to resolution of inflammation. However, volatile anesthetics have not been so far successfully used in the treatment of skin disorders or diseases.
There is a need in the art for improved formulations that may be used in the treatment of dermatological disorders or diseases. There is also a need in the art for improved methods for treating dermatological disorders or diseases. The current invention fulfills these needs.